Motor vehicles, such as, for example, hybrid vehicles use multiple propulsion systems to provide motive power. This most commonly refers to gasoline-electric hybrid vehicles, which use gasoline (petrol) to power internal-combustion engines (ICEs), and electric batteries to power electric motors. These hybrid vehicles recharge their batteries by capturing kinetic energy via regenerative braking. When cruising or idling, some of the output of the combustion engine is fed to a generator (merely the electric motor(s) running in generator mode), which produces electricity to charge the batteries. This contrasts with all-electric cars which use batteries charged by an external source such as the grid, or a range extending trailer. Nearly all hybrid vehicles still require gasoline as their sole fuel source though diesel and other fuels such as ethanol or plant based oils have also seen occasional use.
Batteries and cells are important energy storage devices well known in the art. The batteries and cells typically comprise electrodes and an ion conducting electrolyte positioned therebetween. Battery packs that contain lithium ion batteries are increasingly popular with automotive applications and various commercial electronic devices because they are rechargeable and have no memory effect. Storing and operating the lithium ion battery at an optimal operating temperature is very important to allow the battery to maintain a charge for an extended period of time.
Due to the characteristics of the lithium ion batteries, the battery pack operates within an ambient temperature range of −20° C. to 60° C. However, even when operating within this temperature range, the battery pack may begin to lose its capacity or ability to change or discharge should the ambient temperature fall below 0° C. Depending on the ambient temperature, the life cycle capacity or charge/discharge capability of the battery may be greatly reduced as the temperature strays from 0° C. Nonetheless, it may be unavoidable that the lithium ion battery be used where the ambient temperature falls outside the temperature range.
Alluding to the above, significant temperature variances can occur from one cell to the next, which is detrimental to performance of the battery pack. To promote long life of the entire battery pack, the cells must be below a desired threshold temperature. To promote pack performance, the differential temperature between the cells in the battery pack should be minimized. However, depending on the thermal path to ambient, different cells will reach different temperatures. Further, for the same reasons, different cells reach different temperatures during the charging process. Accordingly, if one cell is at an increased temperature with respect to the other cells, its charge or discharge efficiency will be different, and, therefore, it may charge or discharge faster than the other cells. This will lead to decline in the performance of the entire pack.
The art is replete with various designs of the battery packs with cooling systems. The U.S. Pat. No. 5,071,652 to Jones et al. teaches a metal oxide-hydrogen battery including an outer pressure vessel of circular configuration that contains a plurality of circular cell modules disposed in side-by-side relations. Adjacent cell modules are separated by circular heat transfer members that transfer heat from the cell modules to the outer vessel. Each heat transfer member includes a generally flat body or fin which is disposed between adjacent cell modules. A peripheral flange is located in contact with the inner surface of the pressure vessel. The width of each cell module is greater than the length of the flange so that the flange of each heat transfer member is out of contact with the adjacent heat transfer member. The flanges are constructed and arranged to exert an outward radial force against the pressure vessel. Tie bars serve to clamp the cell modules and heat transfer members together in the form of a stack which is inserted into the pressure vessel.
The metal oxide-hydrogen battery taught by the U.S. Pat. No. 5,071,652 to Jones et al. is designed for cylindrical type of batteries and teaches the heat transfer members in direct contact with the vessel thereby failing to create a clearance between the vessel and the heat transfer members, which can be used to introduce cooling or heating agent to cool or heat the cells.
The U.S. Pat. No. 5,354,630 to Earl et al. teaches a common pressure vessel of a circular configuration type Ni—H.sub.2 storage battery having an outer pressure vessel that contains a stack of compartments. Each of the compartments includes at least one battery cell, a heat transfer member, and a cell spacer for maintaining a relatively constant distance between adjacent compartments. The heat transfer members include a fin portion, which is in thermal contact with the battery cell, and a flange portion which extends longitudinally from the fin portion and is in tight thermal contact with the inner wall of the pressure vessel. The heat transfer member serves to transfer heat generated from a battery cell radially to the pressure vessel.
Similarly to the metal oxide-hydrogen battery taught by the U.S. Pat. No. 5,071,652 to Jones et al., the storage battery taught by the U.S. Pat. No. 5,354,630 to Earl et al. is designed for cylindrical type of batteries. This metal oxide-hydrogen battery teaches the heat transfer members being in direct contact with the vessel thereby failing to create a clearance between the vessel and the heat transfer members which can be used to introduce cooling or heating agent to cool or heat the cells.
The U.S. Pat. No. 6,117,584 to Hoffman et al. teaches a thermal conductor for use with an electrochemical energy storage device. The thermal conductor is attached to one or both of the anode and cathode contacts of an electrochemical cell. A resilient portion of the conductor varies in height or position to maintain contact between the conductor and an adjacent wall structure of a containment vessel in response to relative movement between the conductor and the wall structure. The thermal conductor conducts current into and out of the electrochemical cell and conducts thermal energy between the electrochemical cell and thermally conductive and electrically resistive material disposed between the conductor and the wall structure. The thermal conductor taught by the U.S. Pat. No. 6,117,584 to Hoffman et al. is attached to one or both of the anode and cathode contacts of the cell and not between the cells.
The U.S. Pat. No. 6,709,783 to Ogata et al. teaches a battery pack having a plurality of prismatic flat battery modules constituted by nickel metal hydride batteries, arranged parallel to each other. Each battery module consists of an integral case formed by mutually integrally connecting a plurality of prismatic battery cases having short side faces and long side faces, the short side faces constituting partitions between adjacent battery cases and being shared. A plurality spacers are made of a sheet bent in opposite directions such that alternately protruding grooves or ridges respectively contact the opposite long side faces of the battery modules for providing cooling passages between the battery modules. The battery pack taught by the U.S. Pat. No. 6,709,783 to Ogata et al. is intended to define voids, i.e. the cooling passages between the cells thereby diminishing the packaging characteristics of the pack.
The U.S. Pat. No. 6,821,671 to Hinton et al. teaches an apparatus for cooling battery cells. As shown in FIG. 1 of the U.S. Pat. No. 6,821,671 to Hinton et al., a cooling fin is connected to the battery cell having railings for holding the cooling fin as each cooling fin slides between the railings thereby fitting the cooling fin within the respective battery cell thereby forming the aforementioned apparatus. The engagement of the cooling fin with the battery cell is presented in such a manner that the cooling fins do not extend beyond the battery cells. Thus, cooling agent only serves its intended purpose applicable if introduced from the side of the apparatus. If, for example, the cooling agent is applied to the front of the apparatus, only first battery cell is exposed to the cooling agent thereby preventing effective cooling of other battery cells.
Alluding to the above, FIG. 7 of the U.S. Pat. No. 6,821,671 to Hinton et al. shows the apparatus wherein straps are inserted through ears extending from the cooling fins to connect multiple battery cells to form the apparatus and fins together to keep the battery cells in compression. The straps, as shown in FIG. 7 deform the battery cells thereby negatively affecting chemical reaction between electrolyte, cathodes and anodes of each battery cells and resulting in a reduced life span of the cells.
The Japanese publication No. JP2001-229897 teaches a battery pack design and method of forming the same. The purpose of the method is to create the voids between the cells for cool air to go through the voids and between the cells to cool the cells. Similarly to the aforementioned U.S. Pat. No. 6,709,783 to Ogata et al., the battery pack taught by the Japanese publication No. JP2001-229897 is intended to define the voids between the cells thereby diminishing the packaging characteristics of the pack.
Therefore, there remains an opportunity to improve upon the packs of lithium batteries of the prior art to increase the ambient temperature range at which the lithium battery operates and to provide a new battery pack with improved packaging characteristics.
Also, there remains an opportunity to maintain the battery pack at the optimal operating temperature to ensure the longest possible life cycle, rated capacity, and nominal charge and discharge rates.